Glass compositions intended for the production of panes

ABSTRACT

Glass compositions containing, expressed in percentages by weight, from 0.75 to 1.4% total iron expressed in the form Fe 2  O 3 , from 0.25 to 0.32% ferrous iron in the form of FeO and which has, and at a thickness of between approximately 3 and 3.3 millimeters, exibit a total light transmission factor under illuminent A (TL A ) of at least 70%, a total energy transmission factor (T E ) less than approximately 46% and a transmission factor for ultraviolet radiation (T UV ) less than approximately 25%, and are suitable for the production of windows or panes for use in the architectural field or in automobile and industrial vehicles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to glass compositions adapted for theproduction of windows suitable, especially for use in the architecturalfield or in automobile and industrial vehicles.

2. Discussion of the Background

The windows used for the latter application must satisfy legalrequirements relating to their light transmission. A window intended forthe construction of a windscreen (windshield) must have a total lighttransmission factor under illuminant A (TL_(A)) of at least 75%. Thewindows or panes intended for the construction of the lateral and rearwindows must have, under the same conditions, a TL_(A) factor of atleast 70%.

The glazed area of automobile vehicles is now very large, and clientexpectations with regard to comfort become more and more exacting.Manufacturers of these vehicles are seeking any and every means toreduce the heat experienced by passengers from solar radiation.

To maintain a high light transmission in the visible part of thespectrum while at the same time absorbing as much as possible theremainder of the solar energy, it is known to introduce iron into thecomposition of the glass. Iron is present in the glass both in the formof ferric oxide (Fe₂ O₃) and ferrous oxide (FeO). Fe₂ O₃ in glassenables the absorption of UV radiations and short wavelength radiationin the visible part of the spectrum; in contrast, FeO in glass enablesthe absorption of radiation in the near IR and long wavelength visibleradiation. Although increasing the iron content, in either oxide form,enhances the absorption of the radiation at the two ends of the visiblespectrum, this effect is at the expense of the light transmission.

Various solutions have been proposed for making the most use of the ironoxides to absorb radiation, while at the same time maintaining thehighest possible light transmission. Patent EP-B-297 404 describessilico-sodo-calcic glasses in which the total iron content, expressed inthe form of Fe₂ O₃, is between 0.45 and 0.65%. These glasses areproduced so that at least 35%, and preferably at least 50%, of the totaliron is in the form of FeO. The increase in the FeO content enables theabsorption of glass in the infrared to be increased and the total energytransmission factor (T_(E)) to be reduced. However, when glass ismanufactured in the presence of sulfur in highly reducing conditions, ittakes on an amber color due to the formation of chromophores resultingfrom the reaction between sulfur and ferric iron. To prevent this, it isnecessary to eliminate sulfates in the vitrifiable mixture. Furthermore,since the sulfur content in glass is never zero, the total iron contentmust be rigorously limited to ensure that the percentage of ferric ironremains low. It follows that the capacity of this glass to absorb UVradiations is mediocre.

Glass is known which has a higher total iron content than that specifiedby the above-mentioned European Patent, but still has good lighttransmission and good absorption of infrared and ultraviolet radiation.U.S. Pat. No. 5,214,008 describes glass devoid of ceric oxide and otheroxides of this type, which contains from 0.7 to 0.95% by weight totaliron expressed in the form Fe₂ O₃. This glass is produced inconventional furnaces, from ordinary vitrifiable raw materials. Thedegree of oxidation-reduction of the glass is controlled by theintroduction of carbon and sodium sulfate into the vitrifiable mixture.The oxidation-reduction degree varies within precise limits so that ironin the form of FeO in the glass varies from 0.19 to 0.24% by weight.This glass has a light transmission factor higher than 70%, atransmission factor in the ultraviolet lower than 38% and a total energytransmission factor less than 44.5%, for a thickness of from 3.7 to 4.8millimeters,

Other compositions of silico-sodo-calcic glass for a given thickness,have a light transmission factor of at least 70% and good absorption ofthe infrared and ultraviolet radiation, such as those described inPatent Applications EP-A-488 110 and WO-91/07356. Apart from the ironoxides, the glasses specified in these Patent Applications contain cericoxide and titanium oxide. These oxides enable an increase in theabsorption of ultraviolet radiation. They do, however, havedisadvantages. Cerium oxide is expensive, and its use increases theprice of the glass. Cerium oxide also influences the equilibrium betweenferrous and ferric oxides, reducing the amount of ferrous oxide.Titanium oxide reduces light transmission in the visible range. Thus,there remains a need for a glass that has a high visible lighttransmission, but that transmits much less of other parts of solarradiation.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the present invention to provide aglass for vehicles and buildings that has a high visible lighttransmission, but with a large absorption of infrared and ultravioletradiation.

It is another object of the present invention to provide a glass that isinexpensive to produce and can be poured onto the surface of a bath ofmolten metal.

It is another object of the present invention to provide a glass inwhich the radiation transmission characteristics are mainly controlledby iron oxides.

It is still another object of the present invention to provide a glasswith radiation transmission characteristics superior to the glassespreviously described.

These and other objects, which will become apparent during the followingdetailed description, have been achieved by the inventors discovery thatcompositions of silico-sodo-calcic glass which contain, expressed inpercentages by weight, from 0.75 to 1.4% of total iron expressed in theform of Fe₂ O₃, from 0.25 to 0.32% of ferrous iron in the form of FeO,having a thickness of approximately between 3 and 3.3 millimeters,exibit a total light transmission factor under illuminant A (TL_(A)) ofat least 70%, a total energy transmission factor (T_(E)) less thanapproximately 46% and an ultraviolet radiation transmission (T_(uv))factor less than approximately 25%. The values of light transmission andenergy transmission have been determined by the Parry Moon Mass 2method; the transmission in the ultraviolet has been determined by themethod defined by the standard ISO 9050.

The present invention provides glass which can be poured onto thesurface of a bath of molten metal, with the transmission characteristicsthat are principally regulated by the presence of iron oxides. The glassof the present invention has an absorption of infrared and ultravioletradiation at least equivalent to that of the previously describedglasses, but for a smaller thickness.

The glass according to this invention is prepared from common rawmaterials in conventional furnaces used in the technical field of floatglass production. The melting and refining of the glasses according tothis invention takes place in flame furnaces. If desired, electrodes canbe used to ensure that the glass is heated by the passage of an electriccurrent between the electrodes. The oxidation-reduction degree of theglass is controlled by oxidizing agents, such as sodium sulfate, andreducing agents, such as coke. Other oxidizing agents, such as othersulfates, or Other reducing agents, such as graphite or organicsubstances, could be used. The quantity of sodium sulfate introducedinto the vitrifiable mixture, allowing for the characteristics of thefurnace in which this mixture is melted, is such that the SO₃ content ofthe glass generally lies between 0.10 and 0.35%.

The amount of reducing agents associated with the sulfate, allowing forthe characteristics of the furnace used to produce the glass, iscalculated so that the oxidation-reduction degree of the glass ismaintained within precise limits. These limits are defined by theextreme values of the ratio between the quantity of ferrous ironexpressed in the form of FeO, and the quantity of total iron expressedin the form Fe₂ O₃. According to the invention, this ratio of the weightof FeO/Fe₂ O₃ varies from 22 to 34%; it preferably lies between 25 and30%.

The glass of the present invention does not require the addition ofexpensive materials such as Ce oxide, Ti oxide, or rare earth oxides. Ceoxide and Ti oxide can be limited to less than 0.1%, 0.05%, or even0.01%, based on weight percent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The glass according to this invention is silico-sodo-calcic glass thatcontains the constituents listed below within the following limits,expressed in percentages by weight, based on the total weight of saidglass:

    ______________________________________                                        SiO.sub.2           64 to 75%                                                 Al.sub.2 O.sub.3    0 to 5%                                                   B.sub.2 O.sub.3     0 to 5%                                                   CaO                  2 to 15%                                                 MgO                 0 to 5%                                                   Na.sub.2 O           9 to 18%                                                 K.sub.2 O           0 to 5%                                                   Fe.sub.2 O.sub.3    0.75 to 1.4%                                              (total iron expressed in this form)                                           FeO                 0.25 to 0.32%                                             SO.sub.3            0.10 to 0.35%                                             ______________________________________                                    

The glass according to this invention may contain, in addition, otherconstituents considered as impurities and introduced along with thevitrifiable raw materials employed, and/or by the glass cutletintroduced into the vitrifiable mixture and containing a small quantityof coloring agents other than iron oxides. These impurities amount toless than 0.1% by weight of the glass; they are, for example, titanium,cobalt, nickel, chromium, selenium, manganese or vanadium. Impuritiescan be limited to 0.05% by weight, or even 0.01% by weight. Furthermore,some of these impurities could be reduced to 10 part per million orless.

The amount of the constituents can preferably fall in the followinglimits (weight percent, based on the total weight of said glass):

    ______________________________________                                        SiO.sub.2           68 to 73%                                                 Al.sub.2 O.sub.3    0.3 to 2%                                                 B.sub.2 O.sub.3     0 to 2%                                                   CaO                  4 to 12%                                                 MgO                   0 to 4.5%                                               Na.sub.2 O          10 to 16%                                                 K.sub.2 O           0 to 3%                                                   Fe.sub.2 O.sub.3    0.85 to 1.3%                                              (total iron expressed in this form)                                           FeO                 0.27 to 0.30%                                             SO.sub.3            0.15 to 0.30%                                             ______________________________________                                    

In the glass according to this invention, the total iron content and thecontrol of the respective ferrous oxide and ferric oxide contents,enable a notable absorption of the infrared and ultraviolet radiationwith a relatively small thicknesses. This is especially advantageouswhen the glass is intended for the construction of thin windows.

The transmission characteristics of the glass of the present invention,for a thickness of 3.15 millimeters can preferably be:

    ______________________________________                                               T.sub.E                                                                            45% or less                                                              T.sub.UV                                                                           22% or less                                                       ______________________________________                                    

In addition to the transmission characteristics mentioned earlier, theglass according to this invention has a blue-green tint. The dominantwavelength under illuminant C generally lies between 490 and 505nanometres. Having generally described this invention, a furtherunderstanding can be obtained by reference to certain specific exampleswhich are provided therein for purposes of illustration only and are notintended to be limiting unless otherwise specified.

EXAMPLE

The vitrifiable mixture used for obtaining 100 grams of glass is asfollows:

    ______________________________________                                        sand                  63     g                                                limestone             5.7    g                                                dolomite              21.4   g                                                nephalite             0.90   g                                                sodium carbonate      27.3   g                                                sodium sulfate        0.75   g                                                rouge                 0.9    g                                                coke                  0.035  g                                                ______________________________________                                    

The glass was prepared in a conventional furnace. The analysis of theglass obtained, expressed in percentages by weight, is as follows:

    ______________________________________                                        SiO.sub.2        70.57%                                                       Al.sub.2 O.sub.3 0.62%                                                        CaO              9.50%                                                        MgO              3.90%                                                        Na.sub.2 O       13.90%                                                       K.sub.2 O        0.09%                                                        SO.sub.3         0.18%                                                        Fe.sub.2 O.sub.3 (total iron)                                                                  0.95%                                                        FeO              0.285%                                                       FeO/Fe.sub.2 O.sub.3 (total iron)                                                              0.30%                                                        ______________________________________                                    

The transmission characteristics of this glass, measured as specifiedearlier for a thickness of 3.15 millimeters, are as follows:

    ______________________________________                                                TL.sub.A     71%                                                              T.sub.E      43.5%                                                            T.sub.UV     18%                                                      ______________________________________                                    

This glass has a dominant wavelength under illuminant C of 499nanometres.

The glass according to the invention may be converted into a continuousribbon or band by using the float glass technique. The glass sheetsobtained by cutting this ribbon have thicknesses varying between 1 and 5millimeters. These glass sheets may be used either alone or together toform windows intended, notably, to be mounted in automobiles.

For constructing windscreens or lateral windows or panes, a single sheetof glass, or two glass sheets separated by an intermediate sheet of anorganic material, such as a polymer, are used. The total thickness ofthe glass is most commonly between 3 and 4 millimeters. With thesethicknesses, the glass according to this invention assure goodabsorption of ultraviolet radiation and good thermal comfort.

Like other windows, the windows produced from the glass according tothis invention may be subjected in advance to surface treatments. Thesewindows may be coated, for example, with an organic material such as afilm based upon polyurethanes having antiscratch properties, or a filmassuring a seal in the case of breakage; they also may be coated with anenamel film.

The windows according to this invention may be coated with at least onemetallic oxide film produced by chemical deposition at high temperatureby the techniques of pyrolysis or chemical vapor phase deposition (CVD)or by deposition under vacuum.

This application is based upon the French Patent Application 93/11129,filed Sep. 17, 1993, which is incorporated herein, in it entirety, byreference.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A glass, comprising, in percentage by weight,based on the total weight of said glass:(a) 0.75 to 1.4% total iron,expressed in the form Fe₂ O₃ ; and (b) 0.25 to 0.32% ferrous iron,expressed in the form FeO; wherein said glass has a light transmissionfactor under illuminant A (TL_(A)) of at least 70%, a total energytransmission factor (T_(E)) less than 46%, and a transmission factor forultraviolet radiation (T_(UV)) less than 25%, when said glass has athickness between 3 and 3.3 millimeters, wherein said glass comprisesless than 0.1% of Ce oxide and less than 0.1% of Ti oxide.
 2. The glassof claim 1, wherein said glass has a ratio percentage of the weight offerrous iron in the form FeO, to the total iron expressed in the formFe₂ O₃, of 22 to 34%.
 3. The glass of claim 2, wherein said ratiopercentage is from 25 to 30%.
 4. The glass of claim 1, wherein saidtotal iron, expressed in the form Fe₂ O₃, is from 0.85 to 1.3%.
 5. Theglass of claim 1, wherein said transmission factor for ultravioletradiation (T_(UV)) is less than 22%.
 6. The glass of claim 1, consistingessentially of, in percentages by weight:(a) 0.75 to 1.4% total iron,expressed in the form Fe₂ O₃ ; (b) 0.25 to 0.32% ferrous iron, expressedin the form FeO; (c) 64 to 75% SiO₂ ; (d) 0 to 5% Al₂ O₃ ; (e) 0 to 5%B₂ O₃ ; (f) 2 to 15% CaO; (g) 0 to 5% MgO; (h) 9 to 18% Na₂ O; (i) 0 to5% K₂ O; (j) 0.10 to 0.35% SO₃ ; and (k) less than 0.1% impurities. 7.The glass of claim 1, wherein said glass consists essentially of, inpercent by weight;(a) 0.85 to 1.3% total iron, expressed in the form Fe₂O₃ ; (b) 0.27 to 0.30% ferrous iron, expressed in the form FeO; (c) 68to 73% SiO₂ ; (d) 0.3 to 2 % Al₂ O₃ ; (e) 0 to 2% B₂ O₃ ; (f) 4 to 12%CaO; (g) 0 to 4.5% MgO; (h) 10 to 16% Na₂ O; (i) 0 to 3% K₂ O; (j) 0.15to 0.3% SO₃ ; and (k) less than 0.1% impurities.
 8. The glass of claim7, wherein said glass contains less than 0.05% of said impurities. 9.The glass of claim 6, wherein said glass has a weight ratio percentageof ferrous iron expressed in the form FeO, to total iron expressed inthe form Fe₂ O₃, of 22-34%.
 10. The glass of claim 9, wherein said ratiopercentage is 25-30%.
 11. The glass of claim 6, wherein saidtransmission factor for ultraviolet radiation (T_(UV)) is less than 22%.12. A window, comprising:a first sheet of glass; an organic polymer onsaid first sheet of glass; and a second sheet of glass on said organicpolymer; wherein said first sheet of glass comprises a glass compositioncomprising, in weight percent, (a) 0.75 to 1.4% total iron, expressed inthe form Fe₂ O₃, and (b) 0.25 to 0.32% ferrous iron, expressed in theform FeO, and said glass composition, has a total light transmissionfactor under illuminant A (TL_(A)) of at least 70%, a total energytransmission factor (T_(E)) less than 46%, and a transmission factor forultraviolet radiation (T_(UV)) of less than 25%, when said glasscomposition has a thickness between 3 and 3.3 millimeters, wherein saidfirst sheet of glass contains less than 0.1% of Ce oxide and less than0.1% of Ti oxide.
 13. The window of claim 12, wherein said first glasssheet consists essentially of, in percent by weight:(a) 0.75 to 1.4%total iron, expressed in the form Fe₂ O₃ ; (b) 0.25 to 0.32% ferrousiron, expressed in the form FeO; (c) 64 to 75% SiO₂ ; (d) 0 to 5% Al₂ O₃; (e) 0 to 5% B₂ O₃ ; (f) 2 to 15% CaO; (g) 0 to 5% MgO; (h) 9 to 18%Na₂ O; (i) 0 to 5% K₂ O; (j) 0.10 to 0.35% SO₃ ; and (k) less than 0.1%impurities.
 14. The glass of claim 1, wherein said glass comprises 0.27to 0.32% ferrous iron, by weight, expressed in the form FeO.
 15. Thewindow of claim 12, wherein said transmission factor for ultravioletradiation (T_(UV)) is less than 22%.
 16. The window of claim 12, whereinsaid first sheet of glass comprises 0.27 to 0.32% ferrous iron, inweight percent, expressed in the form FeO.